Bleaching agents have long been used in laundry detergents to enhance the overall cleaning action thereof. Instability of bleaching agents in detergents is mediated principally by metal ion contamination in the detergent themselves, in the wash liquors and in the textiles and fabrics being cleaned. For example, the hydrogen peroxide responsible for the bleaching action in detergent formulas containing a peroxide-based bleaching agent, acts by dissociating into perhydroxyl ion: EQU H.sub.2 O.sub.2 .fwdarw.HOO.sup.- +H.sup.+
This ion attacks the conjugated double bonds which make up most color causing organics or stains. If metal ions (e.g., Cu.sup.II, Fe.sup.III, Mn.sup.II) are present the perhydroxyl ion reacts instead with the hydrogen peroxide causing both species to degrade before they can remove stains. As a result, bleach containing laundry detergents have heretofore been made more efficient by the addition of complexing agents which tie up transition metal ions thus reducing the destructive degradation of the bleaching component.
Examples of conventional acknowledged complexing agents heretofore used in detergents include nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), ethylenediaminetetramethylenephosphonic acid (EDTMP), propylenediaminetetraacetic acid (PDTA), hydroxypropylenediaminetetraacetic acid (HPDTA), hydroxyethanediphosphonic acid, diethylenetriaminetetraacetic acid, diethylenetriaminetetramethylenephosphonic acid, hydroxyethylimino, diacetic acid, hydroxyethylethylenediaminetriacetic acid diethylenetriaminepentaacetic acid and also for example diethanolglycine, ethanolglycine, citric acid, glucoheptonic acid or tartaric acid, as found for example under the heading of Waschmittel in Ullmann's Encyklopadie der technischen Chemie, 4th edition, volume 24, pages 63-160, in particular pages 91-96, Verlag Chemie, Weinheim, 1983.
The action of the existing complexing agents, some of which are used on a large scale, is not always optimal to stabilize bleaching agents in detergent compositions. For instance, NTA makes a very good complexing agent and, in detergents, a fairly good builder for improving the whitening effect and for preventing deposits which cause incrustations and graying on the fabric. However, its performance as a bleach stabilizer is comparatively poor. Even EDTA, despite its good complexing action toward heavy metals, is only a moderate bleach stabilizer in detergents.
In most cases, the biodegradability of prior art complexing agents also leaves something to be desired. For instance, EDTA turns out to be insufficiently biodegradable in conventional tests, as do PDTA, HPDTA and certain phosphonates which, furthermore, are frequently undesirable on account of their phosphorus content.
It is an object of the present invention to provide efficacious bleach stabilizers for detergents which have good complexing properties, is ecologically safe, ideally contains no phosphorus and is readily biodegradable.
It is a related object of the invention to provide a method of stabilizing bleaching agents in detergent formulations by incorporating into said detergent formulations an effective bleach stabilizing amount of a biodegradable nonphosphorus-containing bleach stabilizer.
Further, it is an object of the invention to provide improved detergent formulations containing the biodegradable nonphosphorus-containing bleach stabilizers of the invention.
Other important objects of this invention will become apparent from the ensuing description and appended claims.